Formation of electromagnetic radiation of a second wavelength from electromagnetic radiation of a first wavelength is referred to as wavelength conversion. Wavelength conversion is used in optoelectronic components for color conversion, for example, to simplify generation of white light, for example, in white light-emitting diode flashlights or white light-emitting diode lamps. In this case, for example, blue light, for example, of a light-emitting diode (LED) is converted into green to red light. The color mixture of blue light and green to red light may form white light.
The wavelength conversion may, for example, be carried out by a luminophore formed in the light path of the optoelectronic component, for example, on or over the LED.
A luminophore may be understood as a substance which converts electromagnetic radiation of one wavelength into electromagnetic radiation of another (longer) wavelength with losses, for example, by phosphorescence or fluorescence. The energy difference between absorbed electromagnetic radiation and emitted electromagnetic radiation may be converted into phonons, i.e. heat, and/or by emission of electromagnetic radiation with a wavelength proportional to the energy difference.
Application of the luminophore on or over the optoelectronic component may, for example, be carried out by electrophoretic deposition. To this end, the optoelectronic component, for example, an LED in a package or on a panel may be electrically contacted and immersed in a suspension. The suspension may comprise phosphor particles suspended in a solvent. Phosphor particles may be understood as one type of luminophore. The electrically contacted optoelectronic component in this case forms an electrode. A further electrode may be formed at another position in the suspension. The further electrode may also be referred to as a back electrode.
The phosphor particles in the suspension may have an electric charge on the surface of the particles. The phosphor particles may thereby be moved in an electric field in the direction of the optoelectronic component and deposited as a phosphor layer on the optoelectronic component. The electric field may be formed by application of a potential difference between the electrically contacted optoelectronic component and the back electrode.
During the electrophoretic deposition, phosphor may be simultaneously deposited on all contacted electrically conductive regions of the surface of the optoelectronic component. No phosphor can therefore be deposited on or over electrically insulated surfaces of the optoelectronic component.
One conventional method of applying luminophores, for example, phosphor onto electrically insulated regions of the surfaces of optoelectronic components may be application of an electrically conductive layer onto the electrically insulated region of the surface of the optoelectronic component before the optoelectronic component is immersed in the suspension. To this end, thin metal layers, for example, aluminum layers with a thickness of 100 nm to 200 nm may conventionally be vapor-deposited or sputtered onto the surface of the optoelectronic component.
After electrophoretic deposition of the luminophore layer, for example, a phosphor layer onto the electrically conductive surface of the optoelectronic component, the aluminum may be wet-chemically removed from the surface of the optoelectronic component by an alkaline aqueous solution. The aluminum may be converted into an aluminum salt. The luminophore layer may remain behind on the surface of the optoelectronic component.
Application of the electrically conductive layer onto the surface of the optoelectronic component by vapor deposition or sputtering has, however, the effect that the entire electrically conductive surface is coated with luminophore. Coating of the entire metal-coated surface with luminophore is, however, desirable only for a few applications.
In one conventional method of structuring of the electrically conductive surface of the optoelectronic component, the electrically conductive layer may be structured photolithographically. To this end, before the electrically conductive layer is applied, a photoresist layer may be applied onto the surface of the optoelectronic component and subsequently exposed selectively by a photolithographic mask. The exposed or unexposed regions of the resist layer may then be removed wet-chemically depending on the resist.
The electrically conductive layer may subsequently be deposited on the surface of the optoelectronic component.
The electrically conductive layer on or over the resist layer may then be removed wet-chemically from the surface of the optoelectronic component by dissolving the resist.
The chemical properties of the photoresist and the electrically conductive layer should be formed such that the metal is not simultaneously dissolved with the photoresist. Otherwise, the metal on the regions of the surface of the optoelectronic component without photoresist could also be removed. The choice of available resists and electrically conductive layers may be restricted by the required compatibility of the solubility of the substances of the electrically conductive layer and the resist layer. Furthermore, the dimensions of the optoelectronic component should have only a small difference in relation to the dimension of the mask of the photolithographic process. Otherwise, regions of the surface of the optoelectronic component not meant to be structured could be structured, for example, regions configured as reflectors, overvoltage protection diodes, contact pads or as parts of the package.
In a plurality of optoelectronic components on a common carrier, for example, a panel, it is often not possible to achieve this small tolerance. In other words, the optoelectronic components on a panel may in total have an excessive difference in the dimensions. Photolithographic processes can therefore only limitedly be suitable and used for simultaneous structuring of an electrically conductive layer on or over a plurality of optoelectronic components.
In a further conventional method of structuring an electrically conductive layer, a mask, for example, a shadow mask is used in the particle beam when sputtering an electrically conductive layer on the surface of an optoelectronic component. In this way, an electrically conductive layer can be formed in the regions without a mask. That method may however be very inaccurate and may require different masks for different optoelectronic components.
It could therefore be helpful to provide a process of producing a component and an apparatus that produces a component with which it is possible to limit the electrophoretic deposition to defined regions of the surface of a component.